Sediment Retention in the Floodplain Areas of the Nemunas Catchment

Due to the erosion of the arable surface about 4830000 t/year of soil particles are washed in the Lithuanian territory of the River Nemunas catchment. The main part of this nutrient mud is retained on the grassed surfaces in gullies and sinks, and only less than 5 % of these fine sediments occur in rivers and can be transported downstream into the Curonian Lagoon and the Baltic Sea. They may be intensively accumulated on the sacrificial bottom layer and have markedly negative effect on the environment here. The sedimentation processes in the Nemunas delta, the Curonian Lagoon and the river catchment have been analyzed and the mathematical modeling of the flood activities covering the period of 1950-1991 has been done. It was established that about 3.56 million t/year of sediments were brought by the Nemunas River., About 80% of this amount was deposited and retained in the grassed floodplains. Hydraulic sediment retention measures and pollution reduction possibilities are discussed in the paper.